Solid oxide fuel cells (hereinafter, abbreviated as “SOFC” or simply referred to as “fuel cells”) that use a solid oxide as an electrolyte have been known. An SOFC includes a stack (fuel cell stack) that includes a plurality of stacked single fuel cells each including, for example, an anode and a cathode disposed on the surfaces of a plate-shaped solid electrolyte layer. A fuel gas (for example, hydrogen) and an oxidant gas (for example, oxygen contained in the air) are supplied to the anode and the cathode, respectively. A chemical reaction occurs through the solid electrolyte layer, so that electric power is generated.
In general, the fuel cell is used in a state in which it is connected to a separator separating compartments in which a fuel gas and an oxidant gas are present, respectively. Therefore, a technique for joining the single fuel cell to the separator by Ag brazing filler metal or glass is disclosed (see Japanese Patent No. 03466960).
However, in the case where the single fuel cell is joined to the separator by Ag brazing filler metal, there is a concern that hydrogen and oxygen are diffused in the Ag brazing filler metal and are bonded to each other, whereby voids are generated. When voids are generated, a gas passage may be formed in the Ag brazing filler metal, and a gas may leak.
Further, in the case where the single fuel cell is joined to the separator by glass, diffusion of hydrogen and oxygen in the joint portion can be prevented. In this case, joining strength becomes low because the joint portion of glass is peeled or broken during the formation of a fuel cell stack. This tends to cause a gas leak.
An advantage of the present invention is a separator-fitted single fuel cell and a fuel cell stack in which the reliability of joining and sealing between a single fuel cell and a separator is improved.